1. Field of the Invention
The present invention is directed to intraocular lenses, and more particularly to accommodating intraocular lenses having more than one focus, an extended depth of focus, or enhanced performance through asymmetric transfer of ocular forces in the lenses.
2. Description of the Related Art
A human eye can suffer diseases that impair a patient's vision. For instance, a cataract may increase the opacity of the lens, causing blindness. To restore the patient's vision, the diseased or damaged lens may be surgically removed and replaced with an artificial lens, known as an intraocular lens, or IOL. An IOL may also be used for presbyopic lens exchange or other elective ocular surgical procedures.
Monofocal IOLs have a single focal length, or, equivalently, a single power. Unlike the eye's natural lens, which can adjust its focal length within a particular range in a process known as accommodation, these single focal length IOLs cannot accommodate and thus provide clear vision over a limited range of distances. As a result, distant objects may appear in focus, while objects at a normal reading distance from the eye may appear blurred.
Vision over a broader range of distances can be obtained either through the use of a multifocal lens, which provides different foci configured to produce overlapping focused images for different object distances, or a lens configured to provide an extended depth of focus or depth of field, through for example, an aspheric surface. While such lenses can improve the overall vision range, there may also be an associated reduction in visual acuity or overall visual quality, as well as dysphotopsias.
Another approach is to use an accommodating IOL, which can adjust its axial position, shape, and/or thickness to effect an optical power change within a particular range, similar to the eye's natural lens. As a result, the patient can clearly focus on objects in a range of distances from the eye, rather than at a single distance, or a limited number of set distances. This ability to accommodate is of tremendous benefit for the patient, and more closely approximates the patient's natural vision than a single focal length IOL. One of the challenges in accommodating IOLs is providing a sufficient range of accommodation with the limited amount of ocular force available from the ciliary muscle. Additional challenges with IOLs, including accommodating IOLs include optical aberrations, such as astigmatism, coma, spherical aberration, for example.